A known projection apparatus is a lithographic apparatus. A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of one, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
It has been proposed to utilize immersion lithography, for example using an immersion type lithographic apparatus. As an example, it has been proposed to immerse the substrate in a lithographic projection apparatus in an immersion liquid having a relatively high refractive index, e.g. water, so as to fill the space between the final optical element of the projection lens and the substrate. The point of this is to enable imaging of smaller features because the exposure radiation will have a shorter wavelength in the liquid than in air or in a vacuum. (The effect of the liquid may also be regarded as increasing the effective NA of the system).
Submersing the substrate or substrate and substrate table in a bath of liquid (see for example U.S. Pat. No. 4,509,852) means that there is a large body of liquid that must be accelerated during a scanning exposure. This may require additional or more powerful motors and turbulence in the liquid may lead to undesirable and unpredictable effects.
It has also been proposed to apply a liquid supply system to provide liquid on only a localized area of the substrate and in between the final optical element of the projection system and the substrate (the substrate generally has a larger surface area than the final optical element of the projection system). Ways which have been proposed to arrange for this are disclosed, for example, in WO 99/49504 and EP 1 429 188 A2.